Cutting elements are traditionally utilized for a variety of material removal processes, such as machining, cutting, and drilling. For example, tungsten carbide cutting elements have been used for machining metals and on drilling tools for drilling subterranean formations. Similarly, polycrystalline diamond compact (PDC) cutters have been used to machine metals (e.g., non-ferrous metals) and on subterranean drilling tools, such as drill bits, reamers, core bits, and other drilling tools. Other types of cutting elements, such as ceramic (e.g., cubic boron nitride, silicon carbide, and the like) cutting elements, or cutting elements formed of other materials have also been utilized for cutting operations.
Drill bit bodies to which cutting elements are attached are often formed of steel or of molded tungsten carbide. Drill bit bodies formed of molded tungsten carbide (so-called matrix-type bit bodies) are typically fabricated by preparing a mold that embodies the inverse of the desired topographic features of the drill bit body to be formed. Tungsten carbide particles are then placed into the mold and a binder material, such as a metal including copper and tin, is melted or infiltrated into the tungsten carbide particles and solidified to form the drill bit body. Steel drill bit bodies, on the other hand, are typically fabricated by machining a piece of steel to form the desired external topographic features of the drill bit body.
In some situations, drill bits employing cutting elements may be used in mining environments to drill bolt holes in subterranean formations. Various types of cutting elements, such as PDC cutters, have been employed for drilling boreholes for subterranean support bolts. Although other configurations are known in the art, PDC cutters often comprise a substantially cylindrical or semi-cylindrical diamond “table” formed on and bonded under high-pressure and high-temperature (HPHT) conditions to a supporting substrate, such as a cemented tungsten carbide (WC) substrate.
Subterranean-bolt holes may accommodate support bolts, such as roof bolts, face bolts, or rib bolts, for securing subterranean formations. For example, in underground mining operations, such as coal mining, tunnels are formed underground. In order to make the tunnels safe for use, the roofs of the tunnels must be supported in order to reduce the chances of a roof cave-in and/or to block various debris falling from the roof. In order to support a roof in a mine tunnel, boreholes are typically drilled into the roof using a drilling apparatus. The drilling apparatus commonly includes a drill bit attached to a drilling rod (such as a drill steel). Roof bolts are inserted into the boreholes to secure a roof portion. In some situations, the roof bolts may be used to anchor a support panel or screen to the roof. Support bolts may also be utilized to secure other portions of a mining tunnel, such coal ribs/pillars, side faces, and floors.
Commonly, drilled boreholes may be filled with a resin prior to inserting the bolts, or the bolts may have self expanding portions, in order to anchor the bolts to the roof. Threaded bolts may be problematic to use for securing subterranean features due to their long lengths. Subterranean support bolts commonly extend to eight feet or more in order to adequately secure the formations. Driving a threaded bolt the entire length of a corresponding borehole would require a significant amount of time and energy. Alternatively, widening a portion of the borehole to accommodate a partially threaded bolt, such as a lag bolt, would require multiple drilling operations to be performed using different diameter drill bits in order to bore a single bolt hole, resulting in wasted time and resources.
Often, boreholes for support bolts, such as roof bolts, are drilled into a subterranean formation in a direction that is generally perpendicular to the surface of the formation. Alternatively, a borehole may be drilled at a non-perpendicular angle with respect to the formation surface. For example, a support bolt may extend at an angle through a portion of a coal rib and into an adjacent portion of the roof, thereby stabilizing the coal rib. Unfortunately, starting drilling of a borehole at an angle with respect to a subterranean surface is often difficult since the shape of the drill bit may cause the drill bit to “walk” or wander across the surface, rather than remaining centered at a desired point on the surface.